1. Field of the Invention
The present invention relates to a method of preparing a metal chalcogenide nano-particle or nano-particles, which produces luminescence with a wavelength corresponding to particle size. Particle size of the nano-particle or nano-particles can be freely controlled, and the position where the nano-particle or nano-particles are fixed can be also freely controlled.
2. Description of the Prior Art
Metal chalcogenide, i.e. a compound of a metal such as Cd or Zn with a chalcogen such as S, Se or Te, exhibits semiconducting property and has a band gap in a visible spectral region. Accounting these features, applicability of metal charcogenide to a light-emitting or photo-detecting device has been researched and developed. A metal chalcogenide nano-particle or nano-particles for such the purpose have been chemically mass-synthesized, and fixed as a thin film on a substrate by vapor-deposition or using a proper binder for fabrication of the device.
Since a metal chalcogenide nano-particle or nano-particles have a peculiar band gap dependent on particle size corresponding to wavelength within a region from ultraviolet to visible spectrum, it is expected to provide a light-emitting or photo-detecting device, which enables selection of luminescence or photo-detection within a narrow wavelength region, by severely controlling particle size of the nano-particle or nano-particles. For instance, CdSe, one of semi-conductive metal chalcogenides, can be used as a light-emitting element which produces blue, green or red luminescence corresponding to particle size.
However, metal chalcogenide nano-particles prepared by conventional synthesis have particle size distributed in a broad range, so that its band gap unfavorably extends to a broad visible spectral region. As a result, CdSe produces white luminescence as mergence of blue, green and red lights.
In short, a metal chalcogenide prepared by conventional synthesis merely exhibits properties as aggregate of several thousand semiconductor nano-particles or more with particle size distributed in a broad range. By the way, minimization of nano-particles to tens or several nanometer order has been demanded in response to recent progress and development of semiconductor devices. The aggregate with particle size distributed in a broad range is not material suitable for such the purpose, but provision of nano-particles having function as a quantum dot is strongly demanded. In order to provide such the nano-particles, preparation of metal chalcogenide nano-particles with high freedom with respect to selection of position and particle size is necessarily requested so as to enable fixation of a nano-particle or nano-particles with a proper particle size at a proper position.